Water-based printing ink prepared from polyamide/acrylic graft copolymers

ABSTRACT

A water-dispersible graft copolymer of a polyamide and at least one acrylic monomer is prepared by reacting the polyamide with the acrylic monomer(s) in an alcohol solution in the presence of a free radical peroxidic initiator. The graft copolymer is particularly useful as the resin component of a water-based printing ink.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of Ser. No. 07,166,143, filed Mar. 10, 1988, nowU.S. Pat. No. 4,870,139, which is a continuation-in-part of applicationSer. No. 776,757 filed Sept. 16, 1985 (now abandoned) which in turn is acontinuation-in-part of application Ser. No. 711,219, filed Mar. 13,1985 (now abandoned).

SUMMARY OF THE INVENTION

This invention relates to graft copolymers of polyamides with acrylicmonomers as well as to novel processes for preparing such graftcopolymers. This invention also relates to aqueous varnishes preparedfrom such copolymers as well as to water-based inks prepared from suchaqueous varnishes.

BACKGROUND OF THE INVENTION

The use in printing inks of polyamide resins and of acrylic resins isknown. The use of polyamide resins in inks imparts to them excellentbond strength, adhesion, gloss, and printability. They are not, however,useful for aqueous inks because they are not water-dispersible. On theother hand, acrylic resins can be made water-dispersible, but they donot impart to inks the desirable properties obtainable with polyamides.These two resins are generally incompatible, since upon mixing solutionsof the two they will separate into different phases.

Ideally a copolymer of these two incompatible polymers would result inan excellent water-based ink but such copolymers have not been readilyproduced.

BRIEF DESCRIPTION OF THE INVENTION

Acrylic monomers are grafted onto polyamides resulting in graftcopolymers that retain the desirable properties of each component. Theprocess for preparing the graft copolymers involves reacting thepolyamide with at least one acrylic monomer in an alcohol solvent in thepresence of a free radical peroxidic initiator to obtain an alcoholsolution of the graft copolymer. In order to produce an aqueous varnish,the alcohol solution of the graft copolymer is treated to adjust the pHto at least 7 and then mixed with water. To produce a water-based ink,the desired pigment(s) are mixed with the aqueous varnish and dilutedwith water to the desired tinctorial strength.

DETAILED DESCRIPTION OF THE INVENTION The Polyamide

The techniques for preparing polyamides are well known in the prior art.Such techniques involve combining one or more mono-and/or di-carboxylicacids with one or more monomeric and/or polymeric diamines to form theacid salt; the ratios of acid and diamine components are chosen suchthat a high degree of polymerization will result. The polyamide isreadily obtained by heating the salt so as to release water and form thepolyamide.

Exemplary prior art disclosing polyamides include U.S. Pat. No.3,412,115 which discloses polyamides prepared from a polymeric fattyacid; a hexanoic acid and an alkylene diamine. Other prior art patentsdisclosing polyamides useful for the purposes of this invention includeU.S. Pat. Nos. 3,778,394 and Re. 28,533 as well as British Patent no.1,236,088.

Typically the polyamide is prepared from: (a) a carboxylic acid selectedfrom this group consisting of acids derived from the thermalpolymerization of soya or tall oil fatty acids, C₂ -C₂₅ dicarboxylicacids, C₁ -C₂₄ monocarboxylic acids and mixtures thereof and (b) adiamine selected from the group consisting of monomeric diamines andpolymeric diamines having the respective general formulas H₂ N-R'-NH₂and H₂ N-[R')₂ NH]_(n) (R')₂ -NH₂ and mixtures of such monomeric andpolymeric diamines, wherein R' is a C₂ -C₂₀ aliphatic, aromatic orcycloaliphatic hydrocarbon radical and n=1 to 3.

The thermal polymerization of the soya or tall oil fatty acids willresult in mixtures of dimerized acids, trimerized acids plus higherpolymeric acids as well as unreacted monomeric acids, depending on thenature of the starting material and the reaction conditions. Variousgrades are available ranging from 97 wt. % dimer content to more than 35wt. % trimer content. For the purposes of this invention, it ispreferred that the acids derived from the thermal polymerization of soyaor tall oil fatty acids have a dimeric acid content of about 83 to about95% by weight.

Useful C₂ -C₂₅ dicarboxylic acids include oxalic acid, fumaric acid,maleic acid, malonic acid, succinic acid, glutaric acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid,phthalic acid, isophthalic acid, terephthalic acid, 1,3- and1,4-cyclohexane dicarboxylic acids, naphthalene dicarboxylic acid and C₅-C₂₁ cycloaliphatic dicarboxylic acids. Preferred dicarboxylic acids arealiphatic diacids having at least 6 and preferably 6-12 carbon atomssuch as adipic acid and azelaic acid.

A wide variety of monocarboxylic acids can be employed to preparepolyamides. These may be represented by the general formula: RCOOH whereR- C₁ -C₂₄ alkyl, cycloalkyl or aryl. Representative of alkyl includemethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl and isomersthereof. Examples of cycloaklyl include cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl and the like. The term aryl includes phenyl,naphthyl and alkyl substituted derivatives thereof. Preferredmonocarboxylic acids include acetic acid, propionic acid, 2-ethylhexoicacid, pelargonic acid, decanoic acid, myristic acid, hexadecanoic acid,palmitic acid, stearic acid, oleic acid, linoleic acid, benzoic acid,salicyclic acid and mixtures thereof.

The diamines employed in preparing polyamides include aliphatic,cycloaliphatic or aromatic monomeric diamines of the formula H₂ N-R'-NH₂where R' is a C₂ -C₂₀ aliphatic, aromatic or cycloaliphatic hydrocarbonradical. Among the preferred diamines are ethylenediamine,1,2-propylenediamine, 1,3-propylenediamine, 1,4-diaminobutane,p-xylylenediamine, m-xylylenediamine,piperazines,1,6-hexamethylenediamine, 1,5-pentamethylenediamine,4,4'-methylenebis (cyclohexylamine), 1,2-diaminocyclohexane, 2,2-bis(4-cyclohexylamino) propane, isophoronediamine, polyglycoldiamines,cyclohexanebis (methylamine), bis-1,4-(2'-aminoethyl) benzene and thelike. Polymeric diamines useful in preparing polyamides include thosedefined by the formula: H₂ N--[(R')₂ NH]_(n) (R')₂ -NH₂ where R' isdefined as above and n=1-3. Preferred polymeric diamines in thiscategory are diethylenetriamine, triethylenetetramine,tetraethylenepentamine and the like.

Preferably, the polyamide is prepared from components wherein thecarboxylic acid component comprises a mixture of: (i) acids having adimeric content which are derived from the thermal polymerization ofsoya or tall oil fatty acids, and (ii) a dicarboxylic acid andoptionally (iii) a monocarboxylic acid and the diamine componentcomprises a mixture of monomeric diamines.

Polyamides prepared from a mixture of the acids having a dimeric acidcontent of at least 83 wt. %, azelaic acid and a mixture ofethylenediamine and piperazine or hexamethylenediamine are especiallyuseful for this invention. Also quite useful are those polyamides inwhich the mixture of acids includes a monocarboxylic acid such aspropionic acid.

In those cases where the graft copolymer of the polyamide and theacrylic monomer is to be utilized for preparing an aqueous varnish whichin turn is to be used for preparing a water-based ink, it is essentialthat the polyamide be one which has a weight average molecular weight ofat least about 15,000 (as determined by gel permeation chromatographyusing polystyrene standards). Weight average molecular weights are moreimportant than number average molecular weights for the purposes of thepresent invention, since there is a correlation between the former andhigh bond strengths and other physical properties of water-based inks,whereas number average molecular weights relate to chemical properties.

When graft copolymers based on polyamides having weight averagemolecular weights of at least about 15,000 are employed to preparewater-based printing inks, such inks exhibit high stability and highbond strengths of at least 300 grams per linear inch and in many casesat least 400 grams per linear inch (as measured on an Instron bondstrength tester). High bond and other physical properties of ink filmsare determined by the weight average molecular weight of the polymer. Incontrast thereto, chemical properties of the ink films are determined bythe number average molecular weight of the polymer.

It has been found that with lower weight average moleculer weightpolyamides (i.e. those having weight average molecular weights below15,000) the resultant copolymer has been observed to be less stable inthat the viscosity of the copolymer solution changes upon standingresulting in gellation which sets the mass rendering the copolymersolution unsuitable for an ink formulation. In addition with such lowerweight average molecular weight polyamides, the resultant copolymergenerally exhibits a bond strength of below 300 grams/linear inch asmeasured on an Instron bond strength tester, which is unsuitable for inkapplications, such as a laminating ink, where high bond strength isneeded to prevent the ink from separating from the film surface uponlamination resulting in spotting and decaling.

The Acrylic Monomer(s)

Acrylic monomers useful in the present invention are derivatives ofpropenoic acid (acrylic acid), and 2-methylpropenoic acid (methacrylicacid). Besides the acids themselves, their derivatives, either alone orin combinations, may be used in the present invention.

These derivatives can be represented by the general formula: ##STR1##where R=H or CH₃ and X=OR'or NR"₂

where R'=H,C₁ --C₁₈ alkyl or cycloalkyl, 2-hydroxyethyl, hydroxypropyl,hydroxybutyl or 2-cyanoethyl and R"═H, CH₃, CH₂ OR'''

where R'''═H,CH₃ or C₂ H₅, C₃ H₇, C₄ H₉

Preferably, the acrylic monomer is selected from the group consisting ofmethylmethacrylate, ethylacrylate, hydroxyethylacrylate,hydroxypropylacrylate, ethylmethacrylate hydroxypropylmethacrylate,isobutylmethacrylate, t-butylmethacrylate, isobornylacrylate,isobornylmethacrylate, dicyclopentenyloxyethylacrylate,dicyclopentenyloxyethyl methacrylate, n-butylacrylate,n-butylmethacrylate, acrylic acid and mixtures thereof. The preferredacrylic monomers are those which are free of amino groups which resultin a copolymer which exhibits poor solution stability (gels onstanding).

The polyamide and the acrylic monomer(s) are generally added to thereaction solution in the ratios of about 5-95:95-5 parts by weight, andpreferably in the ratios of about 40-90:60-10 parts by weight ofpolyamide to acrylic monomer(s).

The polyamide and the acrylic monomer(s) components are preferably eachin solution in an alcohol when they are reacted. Any suitable alcoholcan be used, examples including but not being limited to aliphaticalcohols, such as those having 1 to 4 carbon atoms, e.g., methanol,ethanol, propyl alcohol, butyl alcohols, and their mixtures.

Initiators for the free radical grafting of the polyamide and theacrylic monomer(s) include peroxidics such as acyl peroxides, dialkylperoxides, peroxy esters, hydroperoxides, and the like in an amount ofabout 1% to 15% based on the weight of the acrylic monomer(s). Theperoxidic free radical initiators are used as they promote grafting ofthe acrylic monomer(s) onto the polyamide. The peroxy ester is preferredas it promotes higher conversion of acrylic monomer to polymer as wellas a higher degree of grafting onto the polyamide. In comparison, otherfree radical initiators such as azo compounds are unsuitable because ofthe lower conversion of acrylic monomer to polymer and the azo compoundsdo not tend to promote grafting on the polyamide.

The polymerization reaction is basically as follows: ##STR2##

Polyamide+Polyamide-g-Acrylic+Acrylic Polymer. It generally takes placeat a temperature within the range of about 60° to 150° C., andpreferably within the range of about 75° to 115° C. Preferably theresultant copolymer solution has a viscosity of 5 to 250 poises at 40 to50% solids as measured on a Brookfield viscometer at room temperature.

By the process of this invention there is obtained a grafting of atleast one acrylic monomer onto a polyamide backbone, resulting in apolyamide with grafted acrylic side chains. The acrylic monomers aregrafted to the polyamide via abstraction of allylic H atoms onto thedimer acid portion of the polyamide.

By the free radical grafting process of this invention, polyamides andacrylic monomers that normally are incompatible are graft copolymerizedto a product that not only retains the excellent bond strength,adhesion, gloss and printability of the alcohol-soluble polyamide, butalso imparts water dispersability via the grafted carboxyl groups of theacrylic monomer(s) segment, making them extramely suitable for use asvarnishes for water-based, e.g., flexographic and gravure printing inksfor substrates such as packaging films.

For the purposes of preparing an aqueous varnish (i.e. a dispersion orsuspension of the resin component in water), it is desirable that atleast about 15 wt. %, preferably at least 20 wt. %, based on the weightof the resin component, consist of the graft copolymer of the polyamideand the acrylic monomer(s). The remainder of the resin component willcomprise unreacted polyamide and polymers of the acrylic monomer(s). Itis also desirable to neutralize the graft copolymer to a pH of at least7, preferably to a pH in the range of 7 to 10, prior to preparation ofthe aqueous varnish. Since the graft copolymer is acidic in nature,water dispersability is difficult to achieve absent such neutralization.For the purposes of this invention, water-dispersability is intended tomean the ability to form a homogenous aqueous colloidal dispersion asopposed to a non-homogenous dispersion containing at least two phases.

Neutralization of the copolymer is preferably accomplished by an amine.Such neutralization provides a significant advantage in that duringprinting and drying the volatile amines would not be expected to corrodethe equipment as would volatile acids such as hydrochloric acid, aceticacid, etc. which are used to neutralize (and solubilize)amine-functional copolymers common in the art. Preferred amines forneutralization include ammonia, dimethanolamine, diethanolamine,2-methyl-2-aminopropanol, triethylamine, N,N-diethylethanolamine,N,N-dimethyl-2-methyl-2-aminopropanol and the like.

To Prepare the aqueous varnish, the alcohol solution of the graftcopolymer is prepared as described above. From 15 to 40% of the solventis desirably distilled off and the graft copolymer is then neutralizedto a pH above about 7. The resultant solution is then blended with asufficient amount of water in a high speed blender such that there willbe typically 10 to 40 wt. %, preferably 20-30 wt. %, solids (i.e. resincomponent) in the aqueous varnish. If desired, the neutralization andblending with water may take place as a single step, but it is preferredto carry out these steps sequentially.

To prepare a water-based ink from the aqueous varnish, the pigment,aqueous varnish and water (preferably a 4:1 water:ethanol blend) areblended in a high speed mixer or a ball mill. Typically, a water-basedink will contain 5 to 65, preferably 10 to 50 wt. %, based on the totalweight of the ink, of the pigment which may be materials such astitanium dioxide, red lake c cyan blue, diarylide yellow, carbon black,bon red, cyan green. diarylide orange and mixtures thereof. Desirably upto 10 wt. %. based on the weight of the ink, of an anti-foam agent suchas acetylenic diols, octyl alcohols, isopropyl alcohol, silicones etc.is also added. The aqueous varnish is present in the water-based inksuch that there will be 10 to 30 wt. % solids (i.e. resin component),based on the weight of the ink.

This invention is illustrated by the following examples wherein allparts and percentages are by weight (unless otherwise specified).

EXAMPLE 1

(A) 210 parts of a polyamide (weight avg. mol. wt. of 28,000) preparedfrom the thermal polymerization of tall oil fatty acid and having adimeric acid content of about 95 wt. %, azelaic acid, piperazine andethylene diamine and 362.3 parts of n-propyl alcohol were charged into afour-neck round bottom flask under a blanket of nitrogen and slowlyheated to reflux with agitation. At reflux the polyamide was totallydissolved.

Then a mixture of 51.7 parts of methyl methacrylate, 28.5 parts ofglacial acrylic acid, 8.92 parts of hydroxypropyl methacrylate 92.1parts of n-propyl alcohol, and 2.94 parts of benzoyl peroxide was addeddropwise to the polyamide solution over a period of 1-1/4 hour whilemaintaining reflux at 95-100° C.

(B) One hour later, 1/4 of a mixture of 2.68 parts of benzoyl peroxideand 20.7 parts of methyl ethyl ketone were added; and the remainder wasadded incrementally every hour thereafter for 3 hours. Refluxing wascontinued until a determination of solids indicated complete conversionof the acrylic monomers.

The product was then cooled to room temperature and discharged.

The resulting graft copolymer had a weight ratio of 70/30polyamide/acrylic monomers, a solution viscosity of 24 poises at 40%solids, and exhibited good stability in that the solution viscosity didnot change over time.

EXAMPLE 2

(A) 337 parts of the same polyamide as employed in Example 1 and 530parts of n-propyl alcohol were charged into a stainless steel reactor.The mixture was heated to reflux (97° C.) under a blanket of nitrogen.

Then a mixture of 11.9 parts of tert-butyl methacrylate, 11.9 parts ofethyl acrylate, 29.7 parts of glacial acrylic acid, 5.9 parts ofhydroxyethyl acrylate, 59.5 parts of n-propyl alcohol, and 2.0 parts of97% t-butyl neodecanoate was added over a period of one hour underreflux. The batch was held under reflux for an additional hour.

(B) One hour later 1/4 of a mixture of 9.9 parts of n-propyl alcohol and1.8 parts of t-butyl neodecanoate were added and the remainder was addedincrementally every hour thereafter for 3 hours.

The reaction was continued until the product contained 40% nonvolatilesolids. 200 Parts of solvent was then distilled off, the product cooled60° C. and filtered.

The resulting graft copolymer had a polyamide/acrylic monomers ratio of85/15 by weight, a solids content of 50.2%, a viscosity of 121 poises at25° C., and a theoretical acid value of 44, and exhibited good stabilityin that the viscosity did not change over time.

EXAMPLE 3

The procedure of Example 2 was repeated except that the polyamide(weight average molacular weight of 28,000) was prepared with sebacicacid instead of azelaic acid. The resultant graft copolymer solutionexhibited inferior stability compared to the graft copolymer solution ofExample 2 as the viscosity increased over time.

EXAMPLE 4

216.0 Parts of an alcohol-soluble polyamide (weight average molecularweight of 5,000) prepared from ethylene diamine, hexamethylene diamine,propionic acid, and the same fatty acid employed in Example 1 and 329.9parts of n-propyl alcohol were charged into a four-neck round bottomflask under a nitrogen blanket and slowly heated to reflux withagitation. At reflux, the polyamide had totally dissolved.

Then a mixture of 24.0 parts of glacial acrylic acid, 24.0 parts ofn-propyl alcohol, and 0.79 part of benzoyl peroxide was added dropwiseto the polyamide solution over a one-hour period while maintainingreflux at 95-100° C.

(B) One hour later, 1/4 of a mixture of 0.72 part of benzoyl peroxide in6.1 parts of methyl ethyl ketone was added; the remainder was added athourly intervals in 3 equal increments.

(C) Three hours later, a solution of 0.72 parts of benzoyl peroxide in6.1 parts of methyl ethyl ketone was added. Refluxing was continueduntil a solids determination indicated complete conversion of theacrylic monomer.

Twenty percent of the solvent was then distilled off to remove traces ofreactants.

The resulting graft copolymer had a weight ratio of 90/10polyamide/acrylic monomers, a viscosity of 15 poises at 45% solids, butexhibited poor stability in that the viscosity increased over time.

EXAMPLE 5 Flexographic Printing Ink

(A) 60.8 Parts of the product of Example 2 was mixed with 31.8 parts ofwater, 3.4 parts of ethanol, 2.0 parts of 28% aqua ammonia, and 2.0parts of diethylethanolamine.

(B) To 48.5 parts of the neutralized aqueous varnish of part (A) wereadded with high speed mixing 26.1 parts of titanium dioxide and 25.4parts of an 80/20 blend of water/ethanol, resulting in a white ink.

(C) The ink was applied by means of a flexographic hand proofer topolypropylene film. The ink had good printability, gloss, stability,adhesion, a bond strength of at least 400 grams/linear inch as measuredon an Instron bond strength tester, and good crinkle resistance.

EXAMPLE 6

To illustrate the need for graft copolymerizing the acrylic monomer(s)onto the polyamide, the following experiment was carried out:

The procedure of Example 1 was repeated except that the acrylic monomerswere polymerized in the absence of a polyamide. The polymerizedacrylates were then added to the polyamide solution. The two solutionswere incompatible, and precipitation of the acrylic polymers occurred.

EXAMPLE 7

A polyamide/acrylic graft copolymer was prepared as follows:

    ______________________________________                                        (1)     Polyamide           408.0 parts                                               (weight average molecular                                                     weight of about 11,000)                                               (2)     n-propanol          642.6                                             (3)     Isobutylmethacrylate                                                                               14.4                                             (4)     Methylmethacrylate   14.4                                             (5)     Acrylic Acid         36.0                                             (6)     Hydroxypropylacrylate                                                                              7.2                                              (7)     t-butylperoctoate    2.38                                             (8)     n-propanol           72.0                                             (9)     t-butylperoctoate    2.16                                             (10)    n-propanol           12.2                                             ______________________________________                                    

(A) 408 Parts of a polyamide prepared from the same fatty acid as inwith a dimerized acid content of 83% and a trimerized acid content of17%, propionic acid, azelaic acid, ethylene diamine, and hexamethylenediamine and 642 parts of n-propyl alcohol were charged into a four-neckround bottom flask under a blanket of nitrogen and slowly heated toreflux with agitation. At reflux, the polyamide had totally dissolved.

Then a mixture of 14.4 parts isobutylmethacrylate, 14.4 partsmethylmethacrylate, 36.0 parts of glacial acrylic acid, 7.2 parts ofhydroxypropylacrylate, 72.0 parts of n-propyl alcohol, and 2.38 parts oft-butylperoctoate was added dropwise to the polyamide solution over aperiod of 11/4 hour while maintaining reflux at 95-100° C.

(B) One hour later, 1/4 of a mixture of 2.16 parts of t-butylperoctoateand 12.2 parts of n-propanol was added, the remainder was added threetimes at hourly intervals. Refluxing was continued until a determinationof solids indicated complete conversion of the acrylic monomers. Theproduct was then cooled to room temperature and discharged at 45%solids. The resulting graft copolymer had a weight ratio of 85/15 ofpolyamide/acrylic monomers and a solution viscosity of 8 poises, asmeasured on a Brookfield viscomster at 45% solids and at roomtemperature.

    ______________________________________                                        (1)   Polyamide/acrylic graft copolymer                                                                    60.1   parts                                           composition of Example 7                                                (2)   Water                  36.1                                             (3)   Diethylethanolamine    1.9                                              (4)   Ammonium hydroxide solution                                                                          1.9                                              ______________________________________                                    

These ingredients were placed into an Osterizer and mixed forapproximately 15 minutes. The resultant varnish was cooled to roomtemperature and poured off.

    ______________________________________                                        (1)    Varnish (as above)   55.0   parts                                      (2)    Titanium dioxide     25.0                                              (3)    80/20 (w/w) water/ethanol                                                                          10.0                                              ______________________________________                                    

These ingredients were placed into an Osterizer and mixed forapproximately 30 minutes. The resultant ink was cooled to roomtemperature and adjusted to a 25 second reading on a Zahn #2 cup using amixture of 80/20 by weight of water/ethanol as the reducing solvent. ThePH was adjusted to 9.0-9.5 with additional amines as required. The finalink exhibited good printability; however, both stability and bondstrengths of the ink were observed to be inferior. Instability wasexhibited in that after 24 hours the ink exhibited a large increase inviscosity. The laminating bond strength was 50-80 grams/linear inch asmeasured on a Instron bond strength tester.

EXAMPLE 8

    ______________________________________                                        (1)     Polyamide           204.0 parts                                               (weight average molecular                                                     weight of about 15,000)                                               (2)     n-propanol          321.0                                             (3)     Methylmethacrylate   7.2                                              (4)     Isobutylmethacrylate                                                                               7.2                                              (5)     Acrylic Acid         18.0                                             (6)     Hydroxypropylacrylate                                                                              3.6                                              (7)     t-butylperoctoate    1.19                                             (8)     n-propanol           36.0                                             (9)     t-butylperoctoate    1.08                                             (10)    n-propanol           6.10                                             ______________________________________                                    

The reaction was carried out with the same procedure as that used inExample 7. The graft copolymer had a weight ratio of 85/15 ofpolyamide/acrylic monomers and a viscosity of 20 poises at 45% solids.The resultant aqueous ink exhibited good adhesion printability,stability, crinkle resistance (both dry and with water) and blockresistance on polyolefin films. The bond strength was greater than 500grams/linear inch, as measured on a Instron bond strength tester.

EXAMPLE 9

    ______________________________________                                        (1)     Polyamide        204.0                                                        (weight average molecular                                                     weight of about 5,000)                                                (2)     n-propanol       321.3                                                (3)     Methylmethacrylate                                                                             7.28                                                 (4)     Isobutylmethacrylate                                                                           7.2                                                  (5)     Acrylic Acid     18.0                                                 (6)     Hydroxypropylacrylate                                                                          3.6                                                  (7)     t-butylperoctoate                                                                              1.19                                                 (8)     n-propanol       36.0                                                 (9)     t-butylperoctoate                                                                              1.08                                                 (10)    n-propanol       6.10                                                 ______________________________________                                    

The reaction was carried out with the same procedure as that used inExample 7. An ink could not be prepared as the graft copolymer solutionwas unstable resulting in the physical gelling of the varnish.

EXAMPLE 10

    ______________________________________                                        (1)     Polyamide of Example 1                                                                            204.0 parts                                               (weight average molecular                                                     weight of about 28,000)                                               (2)     n-propanol          321.3                                             (3)     Isobornylmethacrylate                                                                              7.2                                              (4)     Isobutylmethacrylate                                                                               7.2                                              (5)     Acrylic Acid         18.0                                             (6)     Hydroxypropylacrylate                                                                              3.6                                              (7)     t-butylperoctoate    1.19                                             (8)     n-propanol           36.0                                             (9)     t-butylperoctoate    1.0                                              (10)    n-propanol           6.1                                              ______________________________________                                    

The reaction was carried out following the procedure of Example 7. Thegraft copolymer had a weight ratio of 85/15 of polyamide/acrylicmonomers and a solution viscosity of 53 poises at 45% solids. Theresultant aqueous ink exhibited good adhesion, printability, stability,crinkle resistance and block resistance with a bond strength of greaterthan 500 grams/linear inch as measured on an Instron bond strengthtester.

EXAMPLE 11

    ______________________________________                                        (1)     Polyamide           210.0 parts                                               (weight average molecular                                                     weight of about 45,000)                                               (2)     n-propanol          363.3                                             (3)     Isobutylmethacrylate                                                                               26.8                                             (4)     Isobornylmethacrylate                                                                              25.0                                             (5)     Acrylic Acid         28.5                                             (6)     Hydroxypropylacrylate                                                                              8.9                                              (7)     t-butylperoctoate    2.94                                             (8)     n-propanol           92.1                                             (9)     t-butylperoctoate    2.68                                             (10)    n-propanol           2.68                                             ______________________________________                                    

The reaction was carried out following the procedure of Example 7. Thegraft copolymer had a weight ratio of 70/30 of polyamide/acrylicmonomers and a viscosity of 200 poises at 45% solids. The resultantaqueous ink exhibited good adhesion, printability, stability, crinkleresistance and block resistance with a bond strength of greater than 400grams/linear inch as measured on an Instron bond strength tester.

EXAMPLE 12

    ______________________________________                                        (1)    Polyamide of Example 1                                                                             168.0 parts                                              (weight average molecular weight                                              of about 28,000)                                                       (2)    n-propanol           288.71                                            (3)    Methylmethacrylate    40.8                                             (4)    Acrylic Acid          24.0                                             (5)    Dimethylaminoethylmethacrylate                                                                      7.2                                              (6)    t-butylperoctoate     2.38                                             (7)    n-propanol            72.0                                             (8)    t-butylperoctoate     2.16                                             (9)    n-propanol            6.1                                              ______________________________________                                    

The reaction was carried out following the procedure of Example 7. Asthe acrylate monomer contained an amino group, the ink prepared from theresultant graft copolymer exhibited poor printability and poor storagestability in that the viscosity increased over time.

EXAMPLE 13

    ______________________________________                                        (1)     Polyamide of Example 1                                                                            210.0 parts                                               (Weight average molecular                                                     weight of 28,000)                                                     (2)     n-propanol          363.3                                             (3)     Isobutylmethacrylate                                                                               26.8                                             (4)     Isobornylmethacrylate                                                                              25.0                                             (5)     Acrylic Acid         28.5                                             (6)     Hydroxypropylacrylate                                                                              8.9                                              (7)     n-propanol           92.1                                             (8)     Azobisisobutyronitrile                                                                             2.94                                             (9)     n-propanol           2.68                                             (10)    Azobisisobutyronitrile                                                                             2.68                                             ______________________________________                                    

The reaction was carried out following the procedure of Example 7. Anink could not be prepared from this varnish due to its lack ofwater-dispersability even after neutralization. This Example illustratesthe importance of the type of free radical initiator employed in thecopolymerization reaction.

What is claimed is:
 1. A water-based printing ink comprising(a) a resin component, said resin component comprising at least about 15 wt. %, based on the weight of the resin component, of a graft copolymer of a polyamide and at least one acrylic monomer, said polyamide having a weight average molecular weight of at least about 15,000, the remainder of the resin component comprising unreacted polyamide and polymers of said acrylic monomer, said graft copolymer having a pH of at least (b) water; and (c) at least one pigment.
 2. The ink of claim 1 wherein the resin component comprises at least 20 wt. % of said graft copolymer.
 3. The ink of claim 1 wherein the resin component is present in an amount of about 10 to about 30 wt. %, based on the weight of the ink.
 4. The ink of claim 1 wherein the graft copolymer has a pH in the range of 7 to
 10. 5. The ink of claim 1 wherein the resin component is present as a solution in alcohol, such solution having a viscosity of about 5 to about 250 poises at about 40 to about 50% solids as measured at room temperature.
 6. The ink of claim 5 wherein the alcohol is C₁ -C₄ aliphatic alcohol.
 7. The ink of claim 1 wherein the pigment is selected from the group consisting of titanium dioxide, red lake c, cyan blue, diarylide yellow, carbon black, bon red, cyan green, diarylide orange and mixtures thereof.
 8. The ink of claim 1 wherein the pigment is present in an amount of about 5 to about 65 wt. %, based on the weight of the ink.
 9. The ink of claim 1 including an anti-foam agent present in an amount up to about 10 wt. %, based on the weight of the ink.
 10. The ink of claim 1 wherein the polyamide is prepared from: (a) a carboxylic acid selected from the group consisting of acids derived from the thermal polymerization of soya or tall oil fatty acids, C₂ -C₂₅ dicarboxylic acids, C₁ -C₂₄ monocarboxylic acids and mixtures thereof and (b) a diamine selected from the group consisting of monomeric diamines and polymeric diamines having the respective general formulas H₂ N-R'-NH₂ and H₂ N-[(R')₂ NH]_(n) -(R')₂ -NH₂ and mixtures of such monomeric and polymeric diamines, wherein R' is a C₂ -C₂₀ aliphatic, aromatic or cycloaliphatic hydrocarbon radical and n=1 to
 3. 11. The ink of claim 10 wherein the acids derived from the thermal polymerization of soya or tall oil fatty acids have a dimeric acid content of about 83 to about 95% by weight.
 12. The ink of claim 1 wherein a carboxylic acid and a diamine are employed in preparing the polyamide such acid comprising a mixture of: (i) acids having a dimeric acid content of at least 83 weight % which are derived from the thermal polymerization of soya or tall oil fatty acids and (ii) a dicarboxylic acid, and such diamine comprising a mixture of monomeric diamines.
 13. The ink of claim 12 wherein the dicarboxylic acid is azelaic acid and the monomeric diamines are ethylenediamine and piperazine.
 14. The ink of claim 1 wherein a carboxylic acid and a diamine are employed in preparing the polyamide such acid comprising a mixture of: (i) acids having a dimeric acid content of at least 83 weight % which are derived from the thermal polymerization of soya or tall oil fatty acids, (ii) a dicarboxylic acid and (iii) a monocarboxylic acid and such diamine comprising a mixture of monomeric diamines.
 15. The ink of claim 14 wherein the dicarboxylic acid is azelaic acid, the monocarboxylic acid is propionic acid and the monomeric diamines are ethylenediamine and hexamethylenediamine.
 16. The ink of claim 1 wherein the acrylic monomer is selected from the group having the general formula ##STR3## wherein R is hydrogen or methyl and X is OR' or NR₂ " in which R' is hydrogen, C₁ -C₁₈ alkyl or cycloalkyl, 2-hydroxethyl, hydroxypropyl, hydroxybutyl or 2-cyanoethyl, and R" is hydrogen, methyl or CH₂ OR''' in which R''' is hydrogen, methyl, ethyl, propyl or butyl.
 17. The ink of claim 16 wherein the acrylic monomer is selected from the group consisting of methylmethacrylate, ethylacrylate, hydroxyethylacrylate, hydroxypropylacrylate, ethylmethacrylate, hydroxypropylmethacrylate, isobutylmethacrylate, tert. butylmethacrylate, isobornylacrylate, isobornylmethacrylate, dicyclopentenyloxyethylacrylate, dicyclopentenyloxyethylmethacrylate, n-butylacrylate, n-butylmethacrylate, acrylic acid and mixtures thereof.
 18. An aqueous varnish comprising:(a) a resin component present as a solution in a C₁ -C₄ alcohol, said resin component comprising at least about 15 wt. %, based on the weight of the resin component, of a graft copolymer of a polyamide and at least one acrylic monomer, said polyamide having a weight average molecular weight of at least about 15,000, the remainder of the resin component comprising unreached polyamide and polymers of said acrylic monomer, said graft copolymer having a pH of at least 7, the resin component being present in an amount of about 10 to about 40 wt. % solids, based on the weight of the aqueous varnish; and (b) water.
 19. The aqueous varnish of claim 18 wherein the resin component is present in an amount of 20 to 30 wt. % solids based on the weight of the aqueous varnish.
 20. The aqueous varnish of claim 18 wherein the resin component comprises at least 20 wt. % of said graft copolymer.
 21. The aqueous varnish of claim 18 wherein the graft copolymer has a pH in the range of 7 to
 10. 22. The aqueous varnish of claim 18 wherein the C₁ -C₄ alcohol solution of the resin component has a viscosity of about 5 to about 250 poises at about 40 to about 50% solids as measured at room temperature.
 23. The aqueous varnish of claim 18 wherein the polyamide is prepared from (a) a carboxylic acid selected from the group consisting of acids derived from the thermal polymerization of soya or tall oil fatty acids, C₂ -C₂₅ dicarboxylic acids, C₁ -C₂₄ monocarboxylic acids and mixtures thereof and (b) a diamine selected from the group consisting of monomeric diamines and polymeric diamines having the respective general formulas H₂ N-R'-NH₂ and H₂ N-[(R')₂ NH]_(n) -(R')₂ -NH₂ and mixtures of such monomeric and polymeric diamines, wherein R' is a C₂ -C₂₀ aliphatic, aromatic or cycloaliphatic hydrocarbon radical and n=1 to
 3. 24. The aqueous varnish of claim 22 wherein the acids derived from the thermal polymerization of soya or tall oil fatty acids have a dimeric acid content of about 83 to about 95% by weight.
 25. The aqueous varnish of claim 18 such diamine comprising employed in preparing the polyamide comprises a mixture of: (i) acids having a dimeric acid content of at least 83 weight % which are derived from the thermal polymerization of soya or tall oil fatty acids and (ii) a dicarboxylic acid, and (b) the diamine comprises a mixture of monomeric diamines.
 26. The aqueous varnish of claim 25 wherein the dicarboxylic acid is azelaic acid and the monomeric diamines are ethylenediamine and piperazine.
 27. The aqueous varnish of claim 18 wherein a carboxylic acid and a diamine are employed in preparing the polyamide such acid comprising a mixture of: (i) acids having a dimeric acid content of at least 83 weight % which are derived from the thermal polymerization of soya or tall oil fatty acids, (ii) a dicarboxylic acid and (iii) a monocarboxylic acid and such diamine comprising a mixture of monomeric diamines.
 28. The aqueous varnish of claim 27 wherein the dicarboxylic acid is azelaic acid, the monocarboxylic acid is propionic acid and the monomeric diamines are ethylenediamine and hexamethylenediamine.
 29. The aqueous varnish of claim 18 wherein the acrylic monomer is selected from the group having the general formula ##STR4## wherein R is hydrogen or methyl and X is OR' or NR₂ " in which R' is hydrogen, C₁ -C₁₈ alkyl or cycloalkyl, 2-hydroxethyl, hydroxypropyl, hydroxybutyl or 2-cyanoethyl, and R" is hydrogen, methyl or CH₂ OR''' in which R''' is hydrogen, methyl, ethyl, propyl or butyl.
 30. The aqueous varnish of claim 29 wherein the acrylic monomer is selected from the group consisting of methylmethacrylate, ethylacrylate, hydroxyethylacrylate, hydroxypropylacrylate, ethylmethacrylate, hydroxypropylmethacrylate, isobutylmethacrylate, tert. butylmethacrylate, isobornylacrylate, isobornylmethacrylate, dicyclopentenyloxyethylacrylate, dicyclopentenyloxyethylmethacrylate, n-butylacrylate, n-butylmethacrylate, acrylic acid and mixtures thereof. 